1. Field of the Invention
This invention relates generally to the field of semiconductor processing. More particularly, the present invention relates to forming photoresist patterns on an exposure field of a semiconductor wafer.
2. Description of the Related Art
The manufacturing of integrated circuit (IC) chips involves many processes. One of the major processes in manufacturing IC chips is photolithography. Photolithography is a process used to transfer masks containing patterns to the surface of a silicon wafer. In a photolithography process, patterns are transferred from a mask to a light sensitive material called photoresist using a light source to print the patterns onto the surface of the wafer. A chemical or plasma etching is then used to transfer the pattern from the photoresist to the surface of the wafer. Fabrication of IC chips may require a number of photolithography processes depending on the complexity of the circuits in the IC chips.
Today, the dimensions of IC components are becoming increasingly smaller. The smaller device dimensions allow more circuit devices to be provided in an IC chip. Accordingly, the precision and accuracy in performing various processes, and photolithography in particular, are critical in producing properly functioning semiconductor IC devices.
In the photolithography process, the printing of mask patterns onto a silicon wafer is typically performed using a projection aligner and stepper device. Conventional projection aligner and stepper device are described in detail in U.S. patent application Ser. No. 09/141,807, entitled xe2x80x9cAn Apparatus and Method for the Improvement of Illumination Uniformity in Photolithographic Systems,xe2x80x9d which is incorporated herein by reference. In using a stepper device, for example, an area in a semiconductor wafer exposed to the stepper device is commonly known as a exposure field. The stepper device xe2x80x9cstepsxe2x80x9d over the fields of the surface of a wafer to print mask patterns.
Unfortunately, printing mask patterns onto wafers using conventional stepper devices often produces variations in critical dimension linewidths across a exposure field. This variation in critical dimension results from a number of factors such as imperfect light illumination, lens, and/or mask in the stepper device. Such variation in linewidths may result in IC chips that are either defective or do not perform to application specification.
In view of the foregoing, what is needed is an apparatus and a method for providing uniform linewidths across the exposure field to improve the yield and performance of IC chips.
Broadly speaking, the present invention fills these needs by providing an apparatus and method for forming a photoresist pattern with a target critical dimension on an exposure field. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, the present invention provides an apparatus for forming a photoresist pattern with a target critical dimension on an exposure field on a semiconductor wafer. The apparatus includes a light source, a lens, and a filter. In the apparatus, the light source is adapted to generate actinic radiation for illuminating a photomask pattern onto the exposure field on the semiconductor wafer. The lens is arranged to focus the actinic radiation from the light source. The filter has a substrate that is transparent to the actinic radiation with the substrate being partitioned into a plurality of regions. One or more regions in the substrate is implanted with a dopant species adapted to absorb the actinic radiation from the lens to change the critical dimension of the one or more regions to the target critical dimension. In this configuration, the plurality of regions in the filter transmits the actinic radiation from the lens to the photomask for illuminating the exposure field on the semiconductor wafer to form a photoresist pattern on the exposure field with the target critical dimension.
In another embodiment, the present invention provides a method for forming a photoresist pattern with a target critical dimension on an exposure field on a semiconductor wafer. In this method, the exposure field is partitioned into a plurality of regions. A set of critical dimension deviation maps is created for a set of line orientations over a first exposure field with one critical dimension map for each line orientation. Each critical dimension deviation map defines an average critical dimension for each of the regions in the exposure field. An average deviation value for each of the regions from the set of critical dimension deviation maps is then evaluated. Based on the average deviation value for each of the regions, an amount of light absorption needed to correct for a critical dimension deviation from the target critical dimension is determined for each of the regions. An absorbing species is then implanted in one or more regions in a transparent substrate to form a filter. The absorbing species is adapted to absorb actinic radiation from a light source to change the critical dimension of the one or more regions in the exposure field to the target critical dimension. The exposure field on a semiconductor wafer is then exposed to the actinic radiation through the filter such that the plurality of regions in the filter transmits the actinic radiation from a lens to a photomask for illuminating the exposure field on a semiconductor wafer to form a photoresist pattern on the exposure field with the target critical dimension.
The absorbing species may be implanted in the filter for use with either a positive or negative resist. When used with a positive resist, the target critical dimension value is the highest critical dimension value selected from the plurality of regions. In this case, the dopant species is implanted to increase the critical dimension of the one or more regions to the target critical dimension. On the other hand, when used with a negative resist, the target critical dimension value is the lowest critical dimension value selected from the plurality of regions. The implanting of the dopant species decreases the critical dimension of the one or more regions to the target critical dimension in this case.
The implanting of filter with light absorbing species provides several advantages. For example, by implanting absorbing species rather than varying the thickness of the filter layer, the phase of the incoming light is not changed. Thus, the filter does not adversely affect lithography. In addition, the filter can be constructed without lithography by scanning the filter under an implant beam at different exposure dosage to impart varying doses of implanted species. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.